1. Field of the Invention
The invention involves a device for metering bulk material which includes a rotor with radial paddles, which rotates around a vertical axle in a cylindrical housing, the housing having a cover plate on its top in which openings are provided for bulk material supply, whereby the rotor has at least one discharge opening following on for bulk material discharge.
2. Description of the Related Art
Bulk materials may be discharged in a metered way with the aid of generally known rotary valves from one area of any desired pressure into an area with either equal, higher or lower pressure. For this the pockets formed between the radial paddles of a rotor rotating around a horizontal axle in a cylindrical housing are filled with bulk material from the top and emptied after a rotation of approximately 180.degree. on the underside.
In the case of another known rotary valve (disclosed in West German Patent Application No. P 34 25 895.7) with a rotor which rotates around a verticle axle, the bulk material is supplied to the rotor chambers via a segment formed opening, to then be emptied through a discharge opening which is arranged eccentrically in the housing bottom after a rotation of approximately 180.degree..
The advantage of the rotary valves with a vertical axle is that they have a large inlet cross section and are therefore also suitable for materials which are not free-flowing and which form bridges. Furthermore the centrifugal force does not act against the flow of the supplied material as opposed to the rotary valves with a horizontal axle.
A disadvantage of the known rotary valves is that especially when metering coarse particle materials, such as plastic pellets for example, particles may become trapped and scraped between the rotor paddles and the edge of the eccentric opening which is directed against the paddle movement. Furthermore, the edges of the rotor paddles are damaged to no little extent due to the scraping and squashing of particles.
A further disadvantage of the known rotary valves with a vertical axle is that the centrifugal force in the case of a discharge opening directed vertically downwards impedes product discharge to such an extent that a part of the material thrown against the cylindrical wall of the housing cannot be discharged from the pockets at all.
In the case of the known rotary valve with verticle axle and discharge opening arranged radially in the housing (disclosed in West German Application No. P 34 25 895.7), the device may only be used in connection with a pneumatic conveying unit. It is, however, often practical to connect several metering units with a combined conveying line, which is practically impossible with the unit already mentioned, as the pneumatically transported material has to be transported through the rotors of the subsequent units, whereby an extremely high pressure loss occurs and plugging of one of the pipe cross sections which lead through the rotary valves may easily occur.